This invention relates generally to improvements in magnetic bearings. More particularly, the present invention relates to a magnetic bearing which provides both radial and axial load support for a shaft.
Electromagnetic bearings are highly effective for supporting a body such as a rotating shaft, which is effectively floated or levitated by magnetic fields. In this way the rotating shaft has no frictional contact with any stationary structure, thereby permitting relatively friction free rotation of the shaft or rotation of a body about the shaft. This arrangement possesses the obvious advantage that there is no mechanical abrasion, which results in reduced mechanical noise and durability not available with other types of bearing structures. Moreover, because of the reduced frictional effects which would otherwise be encountered with conventional bearing structures, it is possible to obtain higher speeds of rotation with electromagnetic bearings.
Magnetic bearings typically require little maintenance and readily lend themselves to operation in hostile environments such as in connection with corrosive fluids where other conventional bearings would be destroyed or rendered inoperable. Further, magnetic bearings are suitable for supporting moving bodies in a vacuum, such as in outer space, or in canned pumps where the pump rotor must be supported without the use of physically contacting bearings.
Conventional electromagnets utilized for energizing levitation gaps are inefficient in that they require a substantial amount of electrical power to generate the required electromagnetic field. In general, prior electromagnetic bearings require large electromagnet coils and control circuitry which have been found to be inherently inefficient. There have been some proposals to use permanent magnets in combination with electromagnets in order to provide greater stabilization and control. However, the conventional prior designs which utilize both electromagnets and permanent magnets are typically inefficient from a spacial standpoint and are considerably complex.
One of the primary considerations in the development of magnetic bearings is to eliminate so-called air gaps. The so-called air gaps form a portion of the magnetic flux pathway of the electromagnets and permanent magnets, and provide a bridge between a supporting structure and a levitated structure. In actuality, some air gaps must be tolerated in order to position a suspended or rotatable body. Thus, air gaps to some extend cannot be avoided, but it is desirable to reduce air gaps to an absolute minimum.
From a pure physics standpoint, an air gap introduces great inefficiency into any type of magnetic structure. An air gap is about 2,000 times less efficient that an iron core medium for transmitting magnetic flux. Thus, in terms of inefficiency, a magnetic bearing structure which has an air gap of 0.1 inch is far more inefficient than a magnetic bearing which has an iron gap of 20 inches.
In some working environments it is desirable to provide radial and thrust load support to a shaft at or adjacent to one end of the shaft only, while permitting rotation of the shaft relative to a stationary housing. Such shaft support lends itself to gimballed mirror, gimballed sensor, or gimballed optics configurations. Further, it is desirable to minimize the number of controls required for complete shaft support and control. U.S. Pat. No. 5,216,308 entitled MAGNETIC BEARING STRUCTURE PROVIDING RADIAL, AXIAL AND MOMENT LOAD BEARING SUPPORT FOR A ROTATABLE SHAFT illustrates a state-of-the-art structure suitable for such working environments. This magnetic bearing structure, however, includes separate radial and axial/moment load bearings to provide the required support for the shaft.
Accordingly, there has a been a need for a novel magnetic bearing capable of providing radial and axial load support to a shaft while permitting rotation of the shaft relative to a stationary housing, which combines the functions of separate radial and axial bearings into a single magnetic bearing structure. Such a novel magnetic bearing should be significantly smaller, lighter and less complex than other similar magnetic bearing systems which utilize separate radial and axial bearings. Additionally, there exists a need for such a magnetic bearing wherein magnetic efficiency of the device is optimized by minimizing air gaps between the levitated and support structures, and which utilizes a permanent magnet bias to reduce power consumption to controlling electromagnet coils. Moreover, there has been a continuing need for such a magnetic bearing which utilizes a combination of radially polarized and axially polarized magnetic fields to produce a compact and spacially efficient structure which obtains a high power efficiency. The present invention fulfills these needs and provides other related advantages.